Coated carrier particles

ABSTRACT

An electrophotographic development carrier comprises core particles coated with a mixture of a fluoropolymer and a modifying material. When utilized with appropriate electroscopic toner materials, the carrier is effective in producing a relatively negative triboelectric charging of the toner particles while it obtains a relatively positive charge. The relatively positive triboelectric characteristic is obtained by curing the coated particles through heating at a temperature less than about 700*F.

lUnite Queener et a1.

COATED CARRIER PARTICLES Inventors: Carl A. Queener; William G.

Ralston; Thomas C. Smith, all of Lexington, Ky.; Joseph 1. Welsh,Austin, Tex.

International Business Machines Corporation, Armonk, NY.

Filed: Oct. 4, 1973 Appl. No.: 403,589

Related U.S. Application Data Division of Ser. No. 110,756, Jan. 28,1971, Pat. No. 3,778,262.

Assignee:

U.S. Cl. 1l7/201,117/17.5,117/100 M, 117/100 S, 96/1 R, 252/621, 260/900Int. Cl. G03g 13/08, G03g 9/02 Field of Search 1l7/l7.5, 100 M, 100 S,117/201, DIG. 6; 252/621; 96/1 R; 260/900 References Cited UNITED STATESPATENTS 6/1963 Rheinfrunk 96/1.4

[451 Mar. 25, 1975 3,507,686 4/1970 Hagenbach 117/168 3,533,835 10/1970Hagenbach 117/16 3,558,492 1/1971 Proskow 96/1.5 3,725,118 4/1973 Fuller117/100 M 3,798,167 3/1974 Kukla 117/100 S 0 Primary Examinerl\/lichae1F. Esposito Attorney, Agent, or FirmJohn W. Girvin, Jr.

[57] ABSTRACT An electrophotographic development carrier comprises coreparticles coated with a mixture of a fluoropolymer and a modifyingmaterial. When utilized with appropriate electroscopic toner materials,the carrier is effective in producing a relatively negativetriboelectric charging of the toner particles while it obtains arelatively positive charge. The relatively positive triboelectriccharacteristic is obtained by curing the coated particles throughheating at a temperature less than about 700F.

6 Claims, No Drawings COATED CARRlER PARTHCLES This is a division ofcopending application Ser. No. 110,756 filed Jan. 28, 1971 now U.S. Pat.No. 2,778,262.

In electrophotography, a photoconductor is charged and then exposedimagewise to light. In the area of the photoconductor exposed to light,the charge dissipates or decays while the dark areas retain theelectrostatic charge.

The difference in the charges between the areas exposed to light anddark areas produces electrical fields therebetween. Accordingly, theresultant latent electrostatic image on the photoconductor is developedby depositing small colored particles, which are known as tonerparticles, over the surface of the photoconductor with the tonerparticles having a charge so as to be directed by the electrical fieldsto the image areas of the photoconductor to develop the electrostaticimage.

A number of means are known for developing the latent electrostaticimage by the application of the toner particles. One of these is knownas cascade development and is described in US. Pat. No. 2,618,552 toWise.

Another means is known as the magnetic brush development process. Thismethod is described in US. Pat. No. 2,874,063 to Greig.

In each of the cascade and magnetic brush development processes, a twocomponent developer material is utilized. The developer materialcomprises a mixture of small toner particles and relatively largecarrier particles. The toner particles are held on the surfaces of therelatively large carrier particles by electrostatic forces, whichdevelop from the contact between the toner and carrier particlesproducing triboelectric charging of the toner and the carrier toopposite polarities. When the developer material is moved into contactwith the latent electrostatic image of the photoconductor, the tonerparticles are attracted to the latent image.

The toner and carrier particles of the developer material are speciallymade and processed so that the toner obtains the correct charge polarityand magnitude of charge to insure that the toner particles arepreferentially attracted to the desired image areas of thephotoconductor. For a given developer-hardware system, the magnitude ofthe triboelectric charge is important in that if such charge is too low,the copy will be characterized by high print density but heavybackground; if the charge is too high, the background is good but theprint density will tend to be low. Thus, there is an optimum range oftoner charge for best overall results.

Prior art dry developer materials, which are employed in an automaticcopy machine, have carrier filming problems due to the recycling of thecarrier particles through many cycles producing many collisions betweenthe carrier particles and between the carrier particles and parts of themachine. The attendant mechanical friction causes some toner material toform a physically adherent film on the surfaces of the coatings of thecarrier particles.

When this occurs, there is a gradual accumulation of permanentlyattached film of toner material on the surfaces of the carrierparticles. This filmed layer of toner tends to impair the normaltriboelectric charging of the toner particles in the developer mixbecause the normal toner-carrier triboelectric charging is partlyreplaced LII by a toner-toner relationship. As a result, the toner,which is available for developing the latent electrostatic image, isless highly charged on the average. If this occurs to a sufficientdegree, the improperly charged toner particles can be deposited on thenonimage areas whereby the quality of the copies is impaired since thenon-image areas possess an unacceptable level of background toner.

When toner filming occurs to a sufficient degree, the entire developermaterial must be replaced thereby increasing the cost of operation ofthe copy machine. Furthermore, it is time consuming. This problem isespecially significant in high speed copy machines in which thousands ofcopy cycles occur in a relatively short period of time or in copymachines in which the developer is continuously agitated.

Furthermore, because of the contact between the carrier particles andbetween the carrier particles and parts of the machine, there isabrasion of the coating of the carrier particles. This abrasion of thecoating also may reduce the effectiveness of the triboelectric chargingbetween the carrier and the toner by exposing the toner to the corematerial of the carrier.

Thus, if the coating is not sufficiently resistant to abrasion, earlyreplacement of the entire developer material is required. Again, thisreplacement of the entire developer material is costly and timeconsuming, especially in high speed copy machines.

Furthermore, even if the coating of the carrier particle resistsabrasion, the coating also must have good adhesion to the core of thecarrier particle. Otherwise, the coating can chip, flake, or spall, evenif the coating is of a material that is not subject to abrasion, due tothe rubbing or contact between the various carrier particles and betweenthe carrier particles and parts of the machine. This also requires earlyreplacement of the developer material.

Therefore, in addition to having the proper triboelectriccharacteristics, the coating of a carrier particle must have goodanti-stick (low surface energy) properties to prevent filming of thecarrier particle by the toner. The coating also must have good adherenceto the core and be resistant to abrasion. Fluoropolymers such asfluorocarbons and fluorosilicones, for example, are materials havinggood anti-stick properties to prevent or greatly inhibit toner filmingthereon as well as being capable of adhering to a core and havingresistance to abrasion.

It has previously been suggested in US. Pat. No. 3,533,835 tol-lagenbach et al. to employ fluorocarbons such aspolytetrafluoroethylene, for example, as a coating for a carrierparticle if finely-divided conductive particles are impacted into thecoating. However, polytetrafluoroethylene, which is sold under thetrademark Teflon by du Pont, has always been described as being at ornear the bottom of any published triboelectric series. In fact, thetrademark Teflon has been used in some published triboelectric series asthe identification of the material rather than polytetrafluoroethyleneor fluorocarbon. The trademark Teflon is employed by du Pont to identifyvarious non-stick finishes including both polymers and/or copolymers offluorocarbons and mixtures of polymers and/or copolymers of afluorocarbon and a modifying resin or material.

Accordingly, materials sold under the trademark Teflon, particularlypolytetrafluoroethylene, have not been considered applicable for use ascarrier coatings in any electrophotographic system in which it isdesired to employ toner particles having a negative triboelectric chargebecause of the location of Teflon, particularly polytetrafluoroethylene,in the various published triboelectric series.

The present invention satisfactorily solves the foregoing problem byproviding a coating of a mixture of fluorocarbon anad a modifyingmaterial on a core so that the carrier particle has the characteristicof being triboelectrically positive with respect to many toners. Becauseof the fluorocarbon in the mixture, which is sold as Teflon, the coatingof the carrier particle has all the desired properties of resistance toabrasion, adherence to the core, and an anti-stick surface so that thefilmed layer of toner cannot form thereon while still having thecharacteristic of being triboelectrically positive with respect tovarious toners.

The present invention achieves this unexpected result by heating thecoating carrier particles at a temperature at which the coating adheresto the core and becomes triboelectrically positive with respect tovarious toners. While it is known that the various materials, which aresold by du Pont under the trademark Teflon, require a curing temperatureto produce a desired finish, there is no suggestionthat controlling thecuring conditions through selecting a curing temperature can produce acoating by the material on a core that results in the coated core beingpositioned substantially high in a triboelectric series so as to bepositive with respect to various materials which may be readily employedas toners in an electrophotographic system whereby the toners may have atriboelectrically negative charge.

The mechanism by which an overall triboelectrically electropositivecarrier is obtained has not been elucidated. It may abe conjectured thatthe inherent electronegativity of the fluorocarbon is simply overriddenby the electropositive modifying material. Possibly such an effect mightbe accentuated by having a heavier concentration of the modifyingmaterial at or near the surface of the coating.

By using the coated carrier particles of the present invention, animproved electrophotographic process is provided. In this improvedprocess, a latent electrostatic image is contacted with a developermixture utilizing the coated carrier particles of this invention.

An object of this invention is to provide a method of forming anelectrophotographic development carrier having a long life while beingtriboelectrically positive with respect to various toners.

Another object of this invention is to provide an electrophotographicdevelopment carrier having a long life while being triboelectricallypositive with respect to various toners.

A further object of this invention is to provide an improvedelectrophotographic process.

The foregoing and other objects, features, and advantages of theinvention will be more apparent from the following more particulardescription of a preferred embodiment of the invention.

The core of the carrier particle formed by the present invention may beany material to which the coating can adhere and can withstand thecuring temperature. Thus, the material of the core of the carrierparticle may be sand, glass beads, or metallic beads, for example.

When the carrier particles of the present invention are employed in adeveloper utilized in the magnetic brush process, the material of thecore is a ferromagnetic material such as iron or steel, for example.Other suitable ferromagnetic materials such as magnetic oxidies andalloys (copper-nickel-iron), for example, may be employed.

The size of the core particles generally may be between 50 and 1,000microns. The preferred size range is between and 600 microns.

The material of the coating of the core of the carrier particle of thepresent invention is formed of a mixture ofa fluoropolymer and amodifying material. While the fluoropolymer may be a fluorosilicone, forexample, it is preferably a fluorocarbon. Furthermore, the fluorocarbonis preferably a copolymer of tetrafluoroethylene and hexafluoropropylenehaving thermal properties very close to the 1:1 copolymer.

Mixtures of the copolymer of tetrafluoroethylene and hexafluoropropylenehaving thermal properties very close to the 1:1 copolymer and amodifying material are sold by du Pont as Teflon. The particular mixtureis identified by numerals as a description thereof.

The coating may be applied to the core by any suitable means such asdipping, spraying, tumbling the cores with a coating solution in abarrel, or through a controlled fluidized bed. The fluidized bed processis preferred since it enables a uniform coating to be applied to thecores of the particles. The fluidized bed process is described in U.S.Pat. Nos. 2,648,609, 2,799,241, and 3,253,944 to Wurster and 3,196,827and 3,241,520 to Wurster et al.

In the Wurster fluidized bed process, for example, the cores aresuspended and circulated in an upwardly flowing stream of heated gassuch as air, for example, in a tower in a manner such that the particlesmove upwardly and are sprayed by the coating material in a first zone.Then, in a second zone, the particles settle through the air stream in azone of lower air velocity and the liquid, which is a solvent and/or adispersant, of the sprayed coating evaporates to leave a thin solidcoating on the particles. The particles recirculate to the first zone sothat successive layers of the coating material are built up on the corein a uniform manner.

After the core has been coated to form the carrier particle, the coatingis cured. After the coating has been appropriately cured, it possessesthe desired triboelectric properties.

Curing of the coating occurs by heating the carrier particles at atemperature below about 700F and preferably above 300F. The particulartemperature would be dependent upon the coating.

The minimum temperature of 300F insures that the coating adheres to thecore. The curing time is preferably about 15 minutes.

The carrier particles are then cooled to a low temperature, preferablyby ambient air cooling. By maintaining the temperature at which thecarrier particles are heated after their cores have been coated to below700F, the carrier particles have an electropositive characteristic eventhough they include a fluoropolymer whereby they would be expected tohave an electronegative characteristic.

The thickness of the carrier coating may vary from 1 to 25 microns.However, it is preferably about 2 to 5 microns. The coating thicknessmust be sufficient to impart the desired triboelectric effect to thecarrier with the upper limit of the thickness being determined byphysical integrity of the coating.

Various suitable pigmented or dyed electroscopic toner materials may beutilized with the carrier, which have the cores of their particlescoated by the coatings of the present invention. The suitability of atoner ma terial to be used in conjunction with these carriers depends onits triboelectric behavior with such carriers.

Examples of materials which are potentially viable as candidate tonersincludes: rosin, gilsonite, phenolformaldehyde resins, rosin modifiedphenolformaldehyde resins, methacrylic resins, polystyrene resins,polyethylene resins, polypropylene resins, epoxy resins, cumarone indeneresin, asphaltum, polyamides, polyurethanes, polyesters, carboxylatedpolyethylene ionomer resins, and mixtures of any of the foregoing.

The following are examples of the present invention in detail. Theexamples are included merely to aid in the understanding of theinvention, and variations may be made by one skilled in the art withoutdeparting from the spirit and scope of this invention.

EXAMPLE I A coating formulation containing a fluoropolymer and amodifying resin, which is sold by du Pont as 954-101 light greenTeflon-S, is diluted about three volumes to one volume with methyl ethylketone by stirring at room temperature and sprayed onto steel beadshaving an average diameter of about 450 microns and a surface suitablyclean for adhesion. The fluoropolymer is a copolymer oftetrafluoroethylene and hexafluoropropylene which has thermal propertiesvery close to the 1:1 copolymer. The modifying resin is epoxy.

The coating formulation of 954-101 light green Teflon-S is a solutionincluding solvents and a pigment in addition to the fluoropolymer andthe modifying resin. The modifying resin is substantially dissolved inthe solvents, which comprise a mixture of methyl isobutyl ketone andxylenes in ratios of 2:3 by weight. The pigment, which is chromic oxide,and the fluoropolymer are cosuspended in the solution of the solventsand the modifying resin. By weight, the fluoropolymer comprisesapproximately 36% of the total solution, the modifying resinapproximately 18.5% of the total solution, the solvents aproximately41.5% of the total solution, and the pigment approximately 4% of thetotal solution.

About 50 milliliters of the diluted material is applied per pound ofsteel beads. The material is sprayed onto the beads in a Wurster cyclicfluidized bed tower at a coating temperature of about 100 F.

The coated cores are then placed in an oven, and the temperature of thebeads is brought to about 575 F. The beads are left at 575 F for aboutminutes and then removed from the oven. The beads are cooled to roomtemperature via ambient air cooling. The coated particles are thenscreened through a US. standard 30 mesh screen to remove agglomerates.

Quantities of this material are now thoroughly mixed with each of threedifferent toners. These are Hunt Graph-O-Print toner sold by Philip A.l-llunt Chemical Corporation, Palisades Park, New Jersey, lBM Part No.1162057 toner, and IBM Part No. 1162051 toner. The resulting developermixes contain by weight about 1% toner and 99% carrier.

The Hunt Graph-O-Print toner comprises a copolymer of styrene/mbutylmetharcrylate resin, polyvinyl butyral plasticizer, and carbon blackpigment. The 18M Part No. 1162057 toner comprises approximately 63.4% byweight of a /30 copolymer of stryene/nbutyl methacrylate resin,approximately 29.1% by weight Amberol 800 (Rhom and Haas) maleicanhydride modified polyester, approximately 1.5% by weight polyvinylstearate plasticizer (Allaco), and approximately 6.0% by weight carbonblack pigment. The IBM Part No. 1 162051 toner comprises a copolymer ofn-butyl metharcrylate/methylmethacrylate resin, maleic anhydridemodified polyester, polyvinyl butyral plasticizer, carbon black pigment,and a fumed silica physically mixed in the toner after compounding.

The charge generated between the toner and the carrier of each of themixtures is measured by cascading portions of the mixture across aninclined slide upon which is imposed an electrostatic voltage patternforming an image and observing the toner weight deposited and the chargethat is displaced by the toner.

The basic component of the charge measuring system is a phenolic circuitboard wherein the copper has been etched so that a center electrode areais isolated from the outer electrode area by a fine etched lined about0.005 inch wide. After making arrangements for electrical contacts tothe electrodes, a /2 mil Mylar sheet is laminated over the copperelectrodes.

The slide is then charged by an AC cut-off corona which has thecharacteristic of supplying current to the test slide only as long as apotential difference exists between the corona screen and the slide.During charging, the center electrode is biased positive or negativedepending on the toner charge polarity being measured.

Since the slide surface potential becomes equal to the screen potential,this serves as a means of repeatedly controlling the charge on theslide. After the Mylar is charged, the two electrodes are returned toground.

The surface potential is then due to the charge trapped on the Mylarsurface and a charge image remains which is quite similar to the chargeimage on a photoconductor. A proximity voltmeter is used to mea sure thevoltage to which the slide is charged. in these tests, i 350 volts wasused depending on the toner charge polarity. it should be understoodthat the Mylar acts as a capacitor so that there is a charge stored onthe test electrode which is of equal magnitude and opposite polarity tothe charge on the Mylar surface.

When the toner-carrier mixture is cascaded over the slide, tonerdeposits over the center electrode and discharges the slide. Theresulting current is fed to an integrating amplifier where the outputvoltage is proportional to the integral of the input current. A 10 faradfeedback capacitor is used giving a calibration factor of 10" coulombscharge per volt output. With the observed voltage output, the chargedisplaced by the toner is easily calculated. The toner weight depositedis easily measured by weighing the slide before and after cascading thetoner-carrier mixture. The charge is calculated by dividing the chargedisplaced by the toner weight deposited and converting to electrons pergram.

The calculated charges are found to be 3.0 to 6.0 X 10 electrons/gram oftoner and the toner charge is negative. Since the toners are negativelycharged to a desired magnitude, the carrier, which has been coated asdescribed above, has served as a functional electropositive carrier withthese toners.

EXAMPLE II A coating formulation containing a fluoropolymer and amodifying resin, which is sold by du Pont as 959-205 dark chocolate onecoat Teflon enamel, is diluted about one volume to one volume with duPont T- 8741 thinner by stirring at room temperature and sprayed ontosteel beads having an average diameter of about 450 microns and asurface suitably clean for adhesion. The fluoropolymer is a copolymer oftetrafluoroethylene and hexafluoropropylene which has thermal propertiesvery close to the 1:1 copolymer. The modifying resin is urethane.

The coating formulation of 959-205 dark chocolate one coat Teflon enamelis a solution including solvents and a pigment in addition to thefluoropolymer and the modifying resin. The modifying resin issubstantially dissolved in the solvents, which comprise a mixture ofmethyl isobutyl ketone and n-methyl-Z-pyrrolidone in ratios of 2:3 byweight with a small amount of water (approximately 5% of the solvents).The pigment, which is iron oxide, and the fluoropolymer are cosuspendedin the solution of the solvents and the modifying resin. By weight, thefluoropolymer comprises approximately 20% of the total solution, themodifying resin approximately 6% of the total solution, the solventsapproximately 71% of the total solution, and the pigment approximately3% of the total solution. The du Pont T-874l thinner is a dilutenthaving the same basic solvent make-up as the solvents in the coatingformulation of the 959-205 dark chocolate one coat Teflon enamel.

About 50 milliliters of the diluted material is applied per pound ofsteel beads. The material is sprayed onto the beads in a Wurster cyclicfluidized bed tower at a coating temperature of about 150F.

The coated cores are then placed in an oven and the temperature of thebeads is brought to about 575F. The beads are left at 575F for aboutminutes and then removed from the oven. The beads are cooled to roomtemperature via ambient air cooling. The coated particles are thenscreened through a US. standard 30 mesh screen to remove agglomerates.

Quantities of this material are now thoroughly mixed with each of threedifferent toners, which are the same as in Example 1. The resultingdeveloper mixes contain by weight about 1% toner and 99% carrier.

The calculated charges, which are determined in the same manner as inExample 1, are found to be 3.0 to 6.0 X 10 electrons/gram of toner. WithHunt Graph-O- Print and IBM Part No. 1162057, the toner charge isnegative, and with IBM Part No. 116205], the toner charge is positive.Since the Hunt Graph-O-Print and [BM Part No. 1162057 toners arenegatively charged to a desired magnitude, the carrier, which has beencoated as described above, has served as a functional electropositivecarrier with these toners. Since the IBM Part No. 1 162051 toner haspositively charged to a desired magnitude, the carrier, which has beencoated as described above, has served as a functional electronegativecarrier with this toner.

EXAMPLE 111 A coating formulation containing a fluoropolymer and amodifying resin, which is sold by du Pont as 958-202 steel blueTeflon-S, is diluted about one volume to one volume with du Pont T-8595thinner by stirring at room temperature and sprayed onto steel beadshaving an average diameter of about 450 microns and a surface suitablyclean for adhesion. The fluoropolymer is a copolymer oftetrafluoroethylene and hexafluoropropylene which has thermal propertiesvery close to the 1:1 copolymer. The modifying resin is urethane.

The coating formulation of 958-202 steel blue Teflon-S is a solutionincluding solvents and a pigment in addition to the fluoropolymer andthe modifying resin. The modifying resin is substantially dissolved inthe solvents, which comprise a mixture of methyl isobutyl ketone andn-methyl-Z-pyrrolidone in ratios of 1:3 by weight. The pigment, which iscobalt aluminate, and the fluoropolymer are cosuspended in the solutionof the solvents and the modifying resin. By weight, the fluoropolymercomprises approximately 16% of the total solution, the modifying resinapproximately 5% of the total solution, the solvents approximately ofthe total solution, and the pigment approximately 4% of the totalsolution. The du Pont T-8595 thinner is a dilutent having the same basicsolvent make-up as the solvents in the coating formulation of 958-202steel blue Teflon-S and contains, by weight, 75% n-methyl-Z -pyrrolidoneand 25% methyl isobutyl ketone.

About 50 milliliters of the diluted material is applied per pound ofsteel beads. The material is sprayed onto the beads in a Wurster cyclicfluidized bed tower at a coating temperature of about 150F.

The coated cores are then placed in an oven and the temperature of thebeads is brought to about 500F. The beads are left at 500F for about 15minutes and then removed from the oven. The beads are cooled to roomtemperature via ambient air cooling. The coated particles are thenscreened through a US. standard 30 mesh screen to remove agglomerates.

Quantities of this material are now thoroughly mixed with each of twodifferent toners. These toners are Hunt Graph-O-Print toner sold byPhilip A. Hunt Chemical Corporation, Palisades Park, New Jersey and IBMPart No. 1162057 toner. The resulting developer mixes contain by weightabout 1% toner and 99% carrier.

The calculated charges, which are determined in the same manner as inExample I, are found to be 3.0 to 6.0 X 10 electrons/gram of toner andthe toner charge is negative. Since the toners are negatively charged toa desired magnitude, the carrier, which has been coated as describedabove, has served as a functional electropositive carrier with thesetoners.

EXAMPLE IV A coating formulation containing a fluoropolymer and amodifying resin, which is sold by du Pont as 955- dark chocolate onecoat Teflon enamel, is diluted about one volume to two volumes with amixture of 60% methyl isobutyl ketone and 40% xylene by weight bystirring at room temperature and sprayed onto steel beads having anaverage diameter of about 450 microns and a surface suitably clean foradhesion. The fluoropolymer is a copolymer of tetrafluoroethylene andhexafluoropropylene which has thermal properties very close to the 1:1copolymer. The modifying resin is methyl phenyl silicone.

The coating formulation of 955-105 dark chocolate one coat Teflon enamelis a solution including solvents and a pigment in addition to thefluoropolymer and the modifying resin. The modifying resin issubstantially dissolved in the solvents, which comprise a mixture ofn-butyl carbitol, methyl isobutyl ketone, and Panasol RX-4(xylenes-technical grade) in the ratio of 4.5:4.5:l by weight. Thepigment, which is red iron (lll) oxide, and the tluoropolymer arecosuspended in the solution of the solvents and the modifying resin. Byweight, the fluoropolymer comprises approximately 17% of the totalsolution, the modifying resin approximately 17% of the total solution,the solvents approximately 62% of the total solution, and the pigmentapproximately 4% of the total solution.

About 13 milliliters of the diluted material is applied per pound ofsteel beads. The material is sprayed onto the beads in a Wurster cyclicfluidized bed tower at a coating temperature of about 130F.

The coated cores are then placed in an oven, and the temperature of thebeads is brought to about 500F. The beads are left at 500F for about 15minutes and then removed from the oven. The beads are cooled to roomtemperature via ambient air cooling. The coated particles are thenscreened through a U.S. standard 30 mesh screen to remove agglomerates.

Quantities of this material are now thoroughly mixed with each of threedifferent toners, which are the same as in Example I. The resultingdeveloper mixes contain by weight about 0.9% toner and 99.1% carrier.

The calculated charges, which are determined in the same manner as inExample I, are found to be 3.0 to 6.0 X 10 electrons/gram of toner andthe toner charge is negative. Since the toners are negatively charged toa desired magnitude, the carrier, which has been coated as describedabove, has served as a functional electropositive carrier with thesetoners.

While Examples 1 to 1V show that the use with particular toners andcorrect heat treatment of the mixture of the fluoropolymer and themodifying material can produce a coating for a carrier particle of adeveloper in which the carrier particles are triboelectrically positivewith respect to the toners, further examples will be given to show thatthe coatings of Examples 1 and 11 have a long life when used in adeveloper simulator.

1n the developer simulator in which the developer mixtures of Examples Vto VII were tested, the developer simulator was a conventional bucketelevator cascade developer. The developer mixture was scooped from areservoir by buckets, elevated to a point above a drum used to simulatea photoconductor drum, cascaded across the drum surface, and thenreturned to the sump by gravity. This cycle, which is continuouslyrepeated, simulates the environment to which a developer mixture issubjected in an operating copy machine.

The following examples were prepared and tested in the developersimulator:

EXAMPLE V A coating formulation containing about 0.6% by weight Orasolred B" dye, sold by Ciba Chemical and Dye Company, Route 208, Fairlawn,New Jersey, and about 4.4% by weight N-type ethyl cellulose, sold byHercules, lnc., Wilmington, Del., dissolved in methyl ethyl ketone bystirring at room temperature is sprayed onto steel beads having anaverage diameter of about 450 microns and a surface suitably clean foradhesion.

About 100 milliliters of the solution is applied per pound of steelbeads. The material is sprayed onto the beads in a Wurster cyclicfluidized bed tower at a coating temperature of about F.

The coated cores are then placed in an oven and the temperature of thebeads is brought to about F and left there for about 24 hours, at whichtime the temperature is raised to about 270F for about an additional onehour. The cured beads are now removed from the oven, cooled to roomtemperature via ambient air cooling, and screened through a U.S.standard 30 mesh screen to remove agglomerates.

A developer mixture, which forms the control sample, is now prepared bythoroughly mixing 0.5% by weight of Hunt Graph-O-Print toner, sold byPhilip A. Hunt Chemical Corporation, Palisades Park, N.J., with thecarrier particles. The resultant developer mixture is now exercised inthe cascade developer simulator.

After 273 hours of such simulation, the carrier is examined. Substantialamounts of coating are missing, and the carrier surface is heavilyfilmed or impacted with toner. Charge imparted to the Hunt Graph-O-Print toner is measured by the method outlined in Examples 1 to IV ontwo samples. One sample is removed from the developer mixture at thebeginning of the simulation and the second sample is removed from thedeveloper mixture at the end of the simulation. The charge of the tonerhas degraded by about 30% during the simulation.

In addition, electrostatic images developed with the EXAMPLE VI The samedeveloper simulator experiment, as performed in Example V, is performedexcept 954-101 light green Teflon-S carrier, prepared as per Example 1,is substituted for the red dyed ethyl cellulose carrier. HuntGraph-O-Print toner at 0.5% by weight is used, and the same developersimulator unit is used.

The carrier is exercised for about 360 hours and then examined. There isno significant filmed-on or impacted toner, and the amount of coatingmissing from. the carrier is minimal.

The charge imparted to the Hunt Graph-O-Print toner is measured by themethod outlined in Examples 1 to IV on two samples. One sample isremoved from the developer mixture at the beginning of the simulationand the second sample is removed from the developer mixture at the endof the simulation. No significant difference is found in the charge.

Copy made with this material in the same copy making robot as referredto in Example Vlll has low background, good print quality, and there isless dusting in the developer unit than in Example V.

EXAMPLE V11 The same developer simulator experiment, as performed inExample V, is performed except 959-205 dark chocolate one coat Teflonenamel carrier, pre pared as per Example 11, is substituted for the reddyed ethyl cellulose carrier. Hunt Graph-O-Print toner at 0.5% by weightis used, and the same developer simulator unit is used.

The carrier is exercised for about 340 hours and then examined. There isno significant filmed-on or iml l pacted toner, and the amount ofcoating missing from the carrier is minimal.

The charge imparted to the Hunt Graph-O-Print toner is measured by themethod outlined in Exampes I to IV on two samples. One sample is removedfrom the developer mixture at the beginning of the simulation and thesecond sample is removed from the developer mixture at the end of thesimulation. A significant but not limiting degradation difference isfound in the charge.

Copy made with this material in the same copy making robot as referredto in Example VIII has low background, good print quality, and there isless dusting in the developer unit than in Example V.

To ascertain the type of copy produced from a developer mixture havingthe carriers prepared in accordance with the presence invention, carrierparticles formed in accordance with Examples I and II were tested in acopy making robot and then compared with a control sample. The copymaking robot is equipped with charging, imaging, developing,transferring, and cleaning stations. The developing station has aconventional bucket cascade developer. The copy making robot uses aphotoconductor of the type employed in the copying machine sold by IBM,the assignee of this application, and described in U.S. Pat. No.3,484,237 to Shattuck et al.

The following examples show the results:

EXAMPLE VIII The carrier particles were prepared in the same way asdescribed in Example V. The only difference being that the HuntGraph-O-Print toner was 0.8% by weight rather than 0.5% by weight.

The resultant developer mixture was placed in the copy making robot andone million copies were made. The carrier performance was monitoredthroughout by observing coating loss, filmed-on or impacted toner, andthe toner concentration required for equivalent print densities atessentially constant photoconductor electrostatics.

After 300,000 copies, the carrier has lost 10% to 15% of its coating,exhibits some filmed-on toner, and must operate at 0.6% to 0.7% byweight toner to give print densities equivalent to those obtained at0.8% to 0.9% toner at the beginning of the test. After one millioncopies, the carrier has lost about 20% to 25% of its coating, is heavilyfilmed with toner, and must operate at 0.3% to 0.4% by weight toner togive print densities equivalent to those obtained at 0.8% to 0.9% tonerat the beginning of the test. This demonstrates that the carriersability to charge toner has been seriously degraded and that operatingconsiderations (toner concentration) has had to have been changed toaccommodate the degradation.

EXAMPLE IX The same copy making robot experiment, as performed inExample VIII, is performed except 954-101 light green Teflon-S carrier,prepared as per Example I, is substituted for the red dyed ethylcellulose carrier. The Hunt Graph-O-Print toner of 0.8% by weight isused, a sister robot with equivalent hardware is used, and the test isrun to one million copies. Again, carrier performance is monitoredthroughout by observing coating loss, filmed-on or impacted toner, andtoner concentration required for equivalent print densities atessentially constant photoconductor electrostatics.

After 300,000 copies, the carrier has lost only about of its coating,has essentially no filmed-on toner, 5 and the toner concentration forequivalent print density has not changed significantly since thebeginning of the test. After one million copies, the carrier has lostonly to 15% of its coating, still has no significant filmed-on toner,and the toner concentration for equivalent print density has not changedsignificantly since the beginning of the test.

EXAMPLE X The same copy making robot experiment, as performed in ExampleVIII, is performed except 959-205 dark chocolate one coat Teflon enamelcarrier, prepared as per Example II, is substituted for the red dyedethyl cellulose carrier. Hunt Graph-O-Print toner of 0.8% by weight isused, and the same copy making robot is used as in Example IX. Again,carrier performance is monitored throughout by observing coating loss,filmed-on or impacted toner, and toner concentration required forequivalent print densities at essentially constant photoconductorelectrostatics.

After 300,000 copies, the carrier has lost only about 5% of its coating,has essentially no filmed-on toner, and the toner concentration forequivalent print density is lower by only 0.1% toner since the beginningof the test. The test was not run to 1,000,000 copies.

The carrier was in better condition at 300,0000 copies than the red dyedethyl cellulose of Example VIII less coating loss and no filmed-on tonerbut not as good as the 954-101 light green Teflon-S of Example IX as thetoner charge (as indicataed by the need to run at slightly lower tonerconcentration) had degraded slightly.

An advantage of this invention is that an electropositive carrier isproduced having a long life. Another advantage of this invention is thattoner filming of a carrier is reduced.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

l. Electrophotographic development carrier particles for use with tonerparticles including:

a plurality of core particles;

a substantially continuous film coating surrounding each of said coreparticles and firmly adhered thereto;

said coating being formed of an inherently triboelectrically negativefluoropolymer and a modifying resin in which said fluoropolymer isessentially insoluble, said fluoropolymer and said modifying resin beingphysically mixed with each other;

60 said carrier particles having a positive triboelectric chargecharacteristic with respect to toner particles formed of IBM part number1162057 and with respect to the toner particles with which said carrierparticles are used.

2. The carrier particles according to claim 1 in which saidfluoropolymer is a fluorocarbon.

3. The carrier particles to claim 2 in which said fluorocarbon is acopolymer of tetrafluoroethylene and hexafluoropropylene having thermalproperties very said modifying material is urethane resin. close to the1:1 copolymer.

4. The carrier particles according to claim-3 in which Said modifyingmaterial is epoxy resin said modifying material lS methyl phenylsllicone resin.

5. The carrier particles according to claim 3 in which 5 6. The carrierparticles according to claim 3 in which

1. ELECTROPHOTOGRAPHIC DEVELOPMENT CARRIER PARTICLES FOR USE WITH TONERPARTICLES INCLUDING: A PLURALITY OF CORE PARTICLES; A SUBSTANTIALLYCONTINOUS FILM COATING SURROUNDING EACH OF SAID CORE PARTICLES ANDFIRMLY ADHERED THERETO; SAID COATING BEING FORMED OF AN INHERENTLYTRIBOELECTRICALLY NEGATIVE FLUOROPOLYMER AND A MODIFYING RESIN IN WHICHSAID FLUOROPOLYMER IS ESSENTIALLY INSOLUBLE, SAID FLUOROPOLYMER AND SAIDMODIFYING RESIN BEING PHYSICALLY MIXED WITH EACH OTHER; SAID CARRIERPARTICLES HAVING A POSITIVE TRIBOELECTRIC CHARGE CHARACTERISTIC WITHRESPECT TO TONER PARTICLES FORMED OF IBM PART NUMBER 1162057 AND WITHRESPECT TO THE TONER PARTICLES WITH WHICH SAID CARRIER PARTICLES AREUSED.
 2. The carrier particles according to claim 1 in which saidfluoropolymer is a fluorocarbon.
 3. The carrier particles to claim 2 inwhich said fluorocarbon is a copolymer of tetrafluoroethylene andhexafluoropropylene having thermal properties very close to the 1:1copolymer.
 4. The carrier particles according to claim 3 in which saidmodifying material is epoxy resin.
 5. The carrier particles according toclaim 3 in which said modifying material is urethane resin.
 6. Thecarrier particles according to claim 3 in which said modifying materialis methyl phenyl silicone resin.